Nowadays, light-emitting diode (LED) as a backlight source of mobile phones, televisions, computers, and other electronic devices, are more popular. In general, a LED module includes a number of LED strings, each LED string is corresponded to a certain display area and is used to illuminate the display area. However, because the characteristic, such as a resistance value of each LED exists difference, thus a current flowing through each LED string would be different even though a voltage applied to each LED string is the same, thereby causing luminance of light emitted by each LED string is different. Therefore, because the luminance of light emitted by each LED string is different, the luminance of the display of the electronic device is unbalanced, which affect the feel of a user, and it is need to adjust that problem.